1. Field of Invention
This invention relates to processes for preparing polymeric materials, and aqueous coating compositions containing the polymeric materials.
2. Prior Art
In recent years, latex paints, i.e., paints based on aqueous dispersions of synthetic organic polymers, have come into widespread use because they can be easily applied, easily cleaned from brushes and rollers, and because they are generally free of objectionable odor.
Materials known as thickeners are commonly used in latex paints, as well as a variety of other coating compositions, to provide thickening effects. An effective thickener should be used in a minimum amount and should not affect the basic properties of the aqueous coating composition in which it is used.
There are many types of thickeners now used in paints and other coating compositions. Water-soluble materials employed as thickeners include natural gums and resins, such as starch, gum arabic, modified starch products, dextrins, sodium alginates, gums, such as tragacanths and other such compounds. Synthetic materials employed as thickeners include carboxymethylcellulose, polyvinyl alcohol, polyacrylamide, polyacrylic acids and salts thereof, methylcellulose and other cellulose derivatives such as carboxymethylcellulose and hydroxyethylcellulose; polyvinylpyrrolidone, polyvinylmethylether, polyethyleneoxides and copolymers of polyvinylmethylether and maleic anhydride. Thickeners of the polyelectrolyte type function primarily due to adsorption and include synthetic polymeric water-soluble thickeners such as the sodium polyacrylates as well as the copolymers of various acrylates, such acrylic thickeners being described more particularly in U.S. Pat. Nos. 2,883,351, 2,956,046, 3,035,004 and 3,436,378.
Water-soluble polyelectrolyte copolymers employed as thickeners include those esters prepared by the esterification reaction between the acid anhydride groups of a copolymer of an alkylvinylether and maleic anhydride with the terminal hydroxyl groups of a nonionic surfactant of an alkylphenoxyethoxyethanol polymer. The resulting water-soluble polymer is a partial ester which contains free acid groups suitable for subsequent neutralization with a basic material, such as an amine or a metal oxide or hydroxide. The water-soluble polymeric esterification materials are employed as emulsion stabilizers, thickeners and film formers. Interpolymers prepared by the reaction of maleic anhydride with vinyl monomers, which interpolymers are useful as thickeners, are described in U.S. Pat. No. 3,499,876, issued Mar. 10, 1970.
Water-soluble, polymeric surfactant thickeners comprising a copolymer of an ester of an alkylarylpolyether alcohol with an unsaturated carboxylic acid compound are described in U.S. Pat. No. 3,708,445, issued Jan. 2, 1973, to Thomas B. Junas et al. While the specification describes these copolymers as containing 70 to 95% of the ester and 5 to 30% of the acid, the examples appear to be suggesting copolymers of 70 to 95% acid and 5 to 30% of the ester.